How The Enriching Circuit, aka Choke, Works

I demonstrate how the enriching circuit works on a Bing CV carburetor.

[@dansmith7617]

This series is SO WELL DONE!! Thank you so much for the time you spent. Things make much more sense now...I never understood how the enricher works. Now I do! -Dan

[@BrooksAirheadGarage]

Thank you for the kind words Dan.

[@foesfly3047]

My limited experience with Bing carbs has been for the 2 that were on a 100 hp Rotax aircraft engine and now a single, 40mm Bing on a Jabiru 85 hp aircraft engine. In these aircraft applications, this feature is not called a Choke, but rather, a Starting Carburetor. I always thought that nomer was odd, since I incorrectly assumed that apparatus simply allowed a richer fuel flow when engaged. You have explained clearly that it actually does function as a simple carburetor by actually mixing and metering fuel and air, independent of the main carb. Thank you.

[@BrooksAirheadGarage]

HI FoesFlyDennis, I was surprised that this is actually a carburetor rather than a restriction in air flow, as is the case with a "choke". When you look at the holes in the disk, it's almost a "digital" device. Clever.

[@59jaguar]

Thanks a lot for making these videos. As a novice mechanic these are Really helpful to understand the mechanics and how things work.

[@BrooksAirheadGarage]

Hi Rodger, Thanks for stopping by. I'm pleased these are helpful to you.

[@janstander4091]

Thank you Sir for a very informative video.I stripped and cleaned my carbs and were uncertain as to how this little discs have been installed originally. You explained it thoroughly and the video is very clear. Thank you once again

[@BrooksAirheadGarage]

Jan, I'm glad this helped out with your carburetor rebuild

[@AdrianWhyte]

This is great! I was having an issue where I couldn’t get the bike to pull fuel into the carbs unless I put my hand over the mouth of the carb whilst cranking the engine. In the end I discovered the boots into the engine were loose and one of the butterflies was partially open, so there was simply a lack of vacuum to make this circuit effective. This all makes sense thanks to your video!

[@BrooksAirheadGarage]

I'm glad this was helpful to you Adrian. Keep those Airheads flying. :-)

[@michaelm8101]

Excellent video. What miserable soul would give this a thumbs down?

[@lulupupupu]

Excellent presentation and explanation. Much appreciate your effort. It helped me understand how the choke on my old solex B30z carburetor works. Thank you.

[@BrooksAirheadGarage]

You’re welcome 😀

[@JanWagner77]

A BIG THANK YOU from Germany for this great explanation video. Now I understand what the Choke actually does.

[@BrooksAirheadGarage]

Hi Jan, That's great. I'm pleased this helped you out.

[@jandl808]

Such a good demonstration. Helps a lot!

[@BrooksAirheadGarage]

Thank J and L. It helps when working on them if you know how they work.

[@stevemiller4352]

Thank you Brooks Garage. I’ve been ‘re-roading’ my Dad’s ‘83 R100RT. It had slid in Wyoming (16 years ago!), & had flopped both sides, so it is resurrected in CS configuration, but it really does run best when both ‘enrichners’ are correctly assembled. Hahaha

[@BrooksAirheadGarage]

Steve, I’m sorry to hear it went down ☹️ it’s nice to hear this material helped get it flying again 😆🏍️

[@seanaguayo]

It always blows my mind that another human created this. Just insane how they figured out the geometry of the angles and tubes, and the math for all the sizes of the holes and needles to perfectly mix gas and air

[@BrooksAirheadGarage]

Sean, indeed, mechanical engineering at it’s best.

[@lulupupupu]

Same!

[@F1Hopeful]

Fantastic. Love your channel!!!!!

[@everettballenger7880]

Excellent concise explanation. More please!

[@Tod_Unctious]

Awesome explanation and detail 👍👏👍👏👍👏👍

[@BrooksAirheadGarage]

Thank you for your kind words Ninja Badger. 🙂

[@LeonardLayne]

Fantastic information. Im a new Rotax owner. Thanks

[@Steve.D]

Great video. Thank you. I've read this info from Motobins "hints". I'm unsure where it otherwise originated from. I wonder if you could comment please? quote: "Cold Starting Problems can often be cured by replacing your old float chamber gaskets unless they provide a really air-tight seal around the choke fuel pick-up tube, the fuel level in the auxiliary chamber will not be raised, and the cold start mixture will not be further enriched during initial operation. The Auxiliary Carburettor itself can often become loose, so being by-passed and ineffective; the resultant air leak will also promote 'surging' at about 40 mph on a small throttle opening change the gasket every few years, and make sure the screws are really tight. "

[@BrooksAirheadGarage]

Steve, That makes sense as the enricher circuit is it's own carburetor and needs a good vacuum to pull fuel into it. When starting, there is very low velocity in the carburetor throat so the vacuum is low and every bit counts.

[@BrooksAirheadGarage]

Steve, yes leaks around the cover of the "enricher" cause these problems. So a broken gasket, gasket that got partially sucked into the enricher, and loose cover screws all create air leaks. As to replacing the gaskets every "few years", I've not seen the need.

[@motooilermotooiler9597]

Excellent ❤❤❤

[@alphashifter2207]

Great stuff! Thank You!

[@BrooksAirheadGarage]

You're welcome.

[@BR.]

VERY NICE! Now I have a stupid question. Those holes, from smaller to larger align to the one in the carb body. But there is a small gap between the holes and when I set the "choke" to 50% I would be right in the middle of the two holes. Or if it's slightly missaligned even at the max it could fall between two holes. Is this assumption correct? Or is the "choke" suppose to have 4 positions that you'd feel with your hand? Mine clearly hasn't anything like that. And how are we normally supposed to use this? Based on outside temperature, a few seconds at max, then a few seconds at mid and all the way down or it doesn't really matter? :)

[@BrooksAirheadGarage]

I start at full choke and then go to half choke after it stumbles a bit because it's too rich. And then down to no choke after a bit, but adjust the throttle to a bit higher RPM using the throttle lock. That's just me. Others may do this differently. There is a detent at about half choke, but I don't feel any other notches except that one.

[@GoatBoy_45-70]

Seems to me there is a kind of hit n miss characteristic built into the alignment of the fuel holes unless there is some kind of detent (locating) system to prevent that ???

[@markstevens7211]

Thanks for a well explained presentation, do you have experience of setting up these carbs to suit pod filters ?

[@BrooksAirheadGarage]

Mark, no I don't. I've learned that BMW designed the intake including the air box to maximize performance of the engine. This information comes from folks who raced these bikes in the 1970's and did dyno testing. Consequently, I conclude that pods (aka K&N filters) degrade performance, although they may look "racey" :-)

[@dieseldan5189]

Terminology: It is not a choke. It is an enricher circuit. There is no choke on this carb. I also used to call it a choke until an engineer corrected me.

[@BrooksAirheadGarage]

Diesel Dan, you are correct. That said those new to airheads call it a choke and do searches using that term. That’s why I titled this with “aka Choke”. In fact it is a separate carburetor that works at low intake velocity and stops working at higher intake velocities.

[@allegrofantasy]

Excellent Tx

[@ivanjukicvk]

Hi. awesome video THNX! Can you tell me please how did you clean this carb like that. What did you use? It looks awesome ...like new!

[@BrooksAirheadGarage]

Ivan, take a look at my site for carburetor rebuild articles (brook.reams.me). I explain how to clean and refurbish the carbs. Sorry about the delay replying to your question.

[@Marc_Wolfe]

Cooool... what vehicle did it come from?

[@BrooksAirheadGarage]

Marc, It’s the same for all 750,900,1000,800,650 airhead engines which use a Bing constant velocity carburetor

[@Marc_Wolfe]

@@BrooksAirheadGarage Right click > don't recommend channel. I asked because I wanted the answer.

[@BrooksAirheadGarage]

@@Marc_Wolfe I believe it was my 1977 BMW R100RS carburetors that I used in the videos on how Bing CV carburetors work.

[@Marc_Wolfe]

@@BrooksAirheadGarage Good to know. There are enough variations with carbs that I never understand why people never put specific info in title or description.

[@BrooksAirheadGarage]

@@Marc_Wolfe The intent of these videos is to explain the theory of operations of all BING CV carburetors, not how to rebuild a specific carburetor. So, the specific bike or BING CV model is really relevant. However, I do show how to rebuild a variety of BING CV carburetors on my website and the specific BMW model they are used on. You can access the site via the link at the top of my KZbin channel page, "Brook's Airhead Garage Website".

[@johncarr123]

Any overhaul videos?

[@BrooksAirheadGarage]

Sure. Go to my site: brook.reams.me. You'll find carb overhaul documentation and how I rebuilt three BMW airheads in great detail. brook.reams.me/bmw-motorcyle-rebuilds/1973-bmw-r755-rebuild-project/bmw-r75-5-bing-carburetor-rebuild/ brook.reams.me/bmw-motorcyle-rebuilds/1977-bmw-r100rs-rebuild-project-index/13-bmw-r100rs-rebuild-refinish-carburetors/

[@sycamorealfinglas4052]

thank you Mr Brooks, i never realised the choke system was as comprehensive as that. your teaching style works on me

[@flobeeonekinobee2353]

The crap ethanol fuel we have now plays havoc with these carbs

[@BrooksAirheadGarage]

Rodger that flobeeone kinobee. I get about 6-8 years out of the o-rings before they deteriorate.

[@flobeeonekinobee2353]

@@BrooksAirheadGarage the water absorbed by the ethanol causes corrosion that can block the tiny drillings before and after the throttle butterfly, if you don't use the bike over the winter months

[@otienokonialaalfred6545]

Sounds like Kelly of Weber university